Composite wxt  clutch



Feb. 7, 1956 J. o. ALMEN ET AL COMPOSITE WET CLUTCH Feb., 7, T956 Original Filed Dec. 20, 1946 J. O. ALMEN ET AL COMPOSITE WET CLUTCH 2 Sheets-Sheet 2 unorncg;

`cilslubrisants.A

United .States Patent O 7.1575512.. Divided and :this application `April 8, 1956, Serial No. litigi/52 s Claims. tot.' raz-11s) 4The :present Iapplisation is a divisional of applicants Serial No. 7l?7.,5.1'2led December 20, 11946, now `forif'e'ited, for "improvementsiniComposite Friction Plate. 'lille` `invention .Irelat'es ttorimproverhents in friction 'clutches andfhrakes adapted to runinoil or other lubricant, and in particular to a composite friction-clutch such Aas"oot1 1d"fl:ie used in fa transmission fdrive 4assembly `such as shovm in Uris. 2,357,295 izo-Earl Thompson, 'issued September 5, i944.

The composite plate ofa friction clutch :corresponding to `the :present inventionasydesctibedibelow consists of 1a :metal fdisc :of either stamped vvstock or :of sintered metal havingfa wearface 'made up :orf fibrous or woven mate- .-rial..V ihermetal may be steel or lother.suitable sheet fstock. Slhe Wearfacetis'fstifiened by theuse off-a plastic V:coating on @the fibers io'f the :thermo-setting type, `applied so as to leave interstitial voids between the fibers, lthe .mat :so :formed `h'aving ifhe 'character of la sponge. An .adhesive lcoating l'ayer :of such thermo-setting plastic is vpreferably placed 'on he supporting metal `disc, the 'whole yheat-'setting :operation talsi'rigpla'ce in an oven :with the composite fdisc .under ifa given :mechanical pressure.

One tobject o thev invention tisl Ito utilize =composite friction discs fsuitabl'e for clutches-and brakes which run in oil bath andare adaptable for either single or mul- `-tiple `#disc runits, theahermokse'tting plastic being lchosen -so fas fro :Ibe :non-sensitive'ito temperature changes M'or 'to ...Inmalt'ing up :platefave Shave found -thatt'he fibers mayfbefofiorganic ormineral'materialsuch as feited y'cellu- .losefpapen synthetic fvisc'oselwool, asbestos, glass wool, fand ,other materials otflikefibrous nature. These :may 'be feither felted :or woven, the tundamentalrequirement being tthatwihenethe vbody fof the material is wetted with a thin :solution of thermoeettinglcement,there V arefispace "voids left rin the lspaces between lthebers in'a'll dimensional directions,LtolpresexveitsA abilityT-to Vpermit inflow and ou't- ;ow fof toil'. This procedure has been 'found ft'o provide stiffness with elasticity iavoidiirgconipacting of the -material which 'would destroy its-porous inature, 'and thus provides `long life I:in @a clutch `subject vto high torques per square .inch o'f surface and to the facton 'of rapidly ciriculat'edflubricant;

lt fan .object iofjthe -linventin lto provide "a special :form :of -Ucln'th whichfembodies v the above-'noted improve- :'mentszin wearifaceshavinglspongecharacteristics, for use fin driveitransmittingdevices equippedwith circulatingoil baths, to provide ialhighidegr'eeof wear life and smoothness of operation, asidescribed further in idetail below.

inthe-:appended:drawings:

`Fig. .v7.1 .is f ag, longitudinal msection f view' l,taken ithm a :trans- :rnissionfassemhly havingja circulatingfil bath, to `show .the `use, of the clutch plates of the `present invention.

Fig. '2 Vis a part section and projection view of a clutch 2,133,798 t patented lFeb. '1,u

plate having lwear surfaces of felted lmat material aflixed to a plain support disc by a thermo-setting bonding layer. Fig. 3 is similar to Fig. 2 except that thesupport disc is made of sintered metal which provides ,greater surface anchorage than the plain disc.

Fig. 4 is a part section of a composite clutchdiscthaving double rings of different forms of wear .facinga to provide differential friction characteristics in. one plate.

Fig. 5 is a View like that of Fig. 1 .in which Ithefelted mat facing is channeled for controlled oil relief. '.Figf shows a form of composite disc vhaving woven mat-facings. Fig. 7 is a view of a wavy disc, so formedto provide a controlled loading interval and tosincrease theaxial elasticity of the stack of clutch discs for desired special loading and unloading characteristics. This disc may be used in the clutch disc assemblies of Fig. '1.

Fig. 1 shows a sectional View of a .transmission-assein bly resembling in all clutch-utilizing details, that described in the aforesaid Letters Patent, U. TS. 2,357,295, issuing September 4, 1944, to Earl A. Thompson.

The engine shaft ilywheel 15 is attached to drum r16 coupled to hollow shaft 17 terminating in vannulus gfe'ar 20 of gear unit A, meshing with planet 'gears 21 supported on carrier 22 attached to hollow shaft 23 axed to lluid flywheel impeller 24. Sun ,gear 26 meshed with .planets `21 is attached to drum 27 externally braked by band 43.0 and internally splined for coned steel clutch discs 31 mating with discs 1 splined on an extension hub-22a of carrier 22.

The iluid ywheel rotor 25 is attached to`shafti3 5 on which is formed the sun gear teeth 42 and 43. -Shaft 3'5 is drilled centrally and radially at 38 and 38a lto' feed oil to the gearing and kto the interior of .the ydrumsisuch as drum 27. Pump drive gear 18 of shaft 17 ,meshes with .gear 19 ofpump shaft 36 driving apumpnconnected to feed oil to the working space of the fluid ilywheel 24, 25 and from thence through passage 37 in hub 25a 'to centralshaft hole 38.

Hollow shaft 23 is drilled radially at convenientfpoints 41, 41 to lead an oil lm under pressure, outwardto the bearings, gears, and to the clutch and brakefaces. Relief holes as indicated at 44, 45 serve to release excess oil reaching the interior of the drums.

The gear unit B has output shaft 50 attached A.to carrier,

nally for clutch plates `32 mating 'with 'plates F1a'2splined.

to hub 57 attached to shaft 23.

-Gear unit C has sun gear 58 attached to-drum 56, and annulus gear 61 meshing with planets 59fsupported on carrier 62 splined to output shaft 450. The annulus gear member 61 is rotatable on an extension offtlie casing 100, and toothed at 63 vfor engagement 'bytoot'hed pawl 65, to stop rotation of annulus v61. I i

The clutch plate groups `of units A and `B 4are Qloaded by fluid pressure applied to the pistons 66 and 67 arid pressure plates 68 and 69 respectively iby external 'fluid feed controls not involved in the present invention. "lh'is pressure may be derived from thepump orfrom another pump which circulates oil to the transmission 'and clutch elements. The body of oil in this system -is retained in the transmission sump from which the pump draws.: "ilihe Y `uum for 45 minutes, for removal of water.

deg. F during distilling action. -F.,untl ready to be used.

4. Apply cement of Formula II to metal disc.

In our process to be given in detail below, we use a cement mixture, as an example, of the following specifications:

Formula I.-Resin (parts by weight) 47 parts phenol crystals 'Y made in accordanceV Ywith the instuction of this speci` fi'lcatiu.Y

reaches 200 deg. F., then distill under maximum vac- Agitate mixture constantly during both operations, maintaining bath at boiling temperature of water. At peak of reuxing,rresin temperature is held at 210 deg. F., dropping to 204 deg. F. at end of reuxing. In distillation, resin temperature may drop to 120 deg. F. and rise to 160 Store resin at 50 deg.

Formula Il.-Cement (parts by weight) 115 parts resin of Formula I.

150 parts propylalcohol (for visc. 90400 deg. M.) 50 parts China clay (selected kieselguhr) 6 parts powdered hexa-methylene-tetramine Stir-mix thoroughly to dissolve hexa., adding China :'clay after solution mix is clear and not lumpy. Store at 1. Mix equal volume of resin of Formula I with isopropyl alcohol which will give a solution of 20 to 25 pct. solids ratio after evaporation.

2. Impregnate felted rings in solution of step l for 2 to 3 minutes. tion.

3'.- Dry in oven at 200 deg. F. for 30 minutes. Test for spongy nature of ring.

Wipe off -excess to 0.005 thickness. Pre-dry with 5 minute infra-red exposure. Bonding layer should be slightly 5. Assemble driedimpregnated rings of step 3 with cement coated discs of step 4. Press mechanically to Yremove air bubbles and initiate adhesion of rings to disc.

6. Bake 20 minutes at 300 deg. F., in air circulation furnace.

`7. Clean baked article of excess cement, including droplets on faces of felted discs.

The above formulas for producing the complete clutch disc of the present invention are not to be understood as restricting the scope of the invention-but are given :to make the invention wholly clear in principle.

One skilled in the art, with these instructions is able to reproduce the invention in different forms. Other resins and solvents may be utilized without departing from the teachings herein, and variations and modifications of the procedural steps given in Formula III are likewise available to the skilled worker in this iield.

In Formula III, Vfor example, step 4 maybe replaced by substitution of a bonding layer ring cut from a sheet or lm of plastic having the Formula II and assembled between metal disc and the felted, impregnated ring in Centrifugally spin off excess resin solu-V step 5. 'In this a light coat of wet cement maybe given the metal disc to promote bonding, prior to mechanical pressing for initial adhesion.

f -The stiiening mixtures noted above maybe almost water thin, and are soaked intov the formedrough discs :which have been cut from sheet stock to desired shape.

After this wetting, the rough discs are air dried, which process may be accelerated by the'blowing'oi de-Vhumidi- 1 fied warmed air upon them. The thinner`ing`redients evaporate, leaving each of the fibers encased in a sheath of the plastic, with plastic joints at the points of intersection of the bers. When the felted piece is dry it is laid over a coating of plastic cement formed on the supporting metal plate, of the same general formulation as that originally used in wetting the felted plate, but the coating mixture contains less of the solvent thinner. This coating is iirst wiped with a blade at uniform pressure to remove the excess, and is then ready for afiixing the felted piece or mat to the metal disc, which may be of iron, steel, bronze or other alloy.Y

The metal discs are chemically or otherwise cleaned, and may be coated with the heavier bodied cement prior to applying the rough wear-face disc; the latterdisc is then applied to the metal disc under controlled light mechanical pressure to squeeze out the air bubbles so as to form a tight bond with the metal, and theassembly is then inserted in an oven, and maintained'in a spacer clamp under light mechanical pressure, for a predetermined baking period at relatively low temperatures in the range of 290 to 310 deg. F. The spacer arrangement is to control the degree of mechanical pressure Yforavoidance of compacting. The degree of holding or xture pressure may be only a few pounds, much'less than the heavy mold pressures ordinarily used Vin this art which are normally from 300 to 1000 pounds persquare inch, for solid mold end products. L

After cooling and inspection, the composite .plateis ready for use. Instead `of the adhesive coatingbeing applied in liquid form, this material may .be cutA in a dried lm state and placed between felted Vdisc and support plate prior to heat assembly in the final setting operation. In the figures Ythe numerals 4V and 4a denote the bondinglayer, applied either in iiuid or` dry form.

, For discs requiring wear-faces on both sides, the second rough disc is aixed to themetal disc in the same manner as outlined aboveand the assemblyis then baked as a unit.

YSo as to provide some. specific examples Vof the objects and advantages it is deemed useful to describe in exact detail at least one article andvv sequence of making it for properinstruction to those skilled in the art. In Figure 2 we show a broken-away projection view ofr a portion of a typical clutch plate. Ametalv plate 1, -which may be of bronze, steel, cast-iron or other useful alloy, is madeY chemically or mechanically cleanl prior to succeeding operations combining it Ywith the wear-surface discs 2 vand 2a. The splines Srare for the purpose of requiring the composite clutch disc to rotate with a drum as a part of a drive assembly. The spline teeth may also be formed in the outer periphery, as is shown in Fig-4.

The nished article as sectioned inFigure 1Y shows the central plate 1 with the spongy wear surfaces attached to both faces, the bonding layer 4 being emphasized. It will be` understood by those skilled in the art that the plastic bonding layers 4 and 4a made up;-as described above, and thermo-set by application of heat, has an.in timate relationshipy with ,the surface crystal` formation of the metal strip and with-the brous body of the attached or cemented working face.. This gives a homo- Y geneous bond not otherwise readily obtained, and tends to v.prevent local lolsslofl adhesion by the uniform nature of the whole plastic bond body of plater and fibers.

be somewhat different, due to the fact that it may be undesirable to trap or pocket bodies ofplastic, oil or thinner inside the metal sponge of the sintered plate 10. To guard against this undesired result, the sintered plate y10 may be Yslightly wettedwith the thermo-plastic combination given above in the Formulas Iand Il', and centrifugally dried, ,so that duringltheksucceeding oven operation'the pore sysf in the body 2, cemented thereon. In practice, it is des'rable to driveV vott the 4excess thinners by evaporation with warmed, vdried air, over a longer time than normally Vrequired for the drying of the ielted paper bodies 2 and 2a alone. The operator should have no particular diiiic'ulty in lusing the sintered plate, if such be desirable.

' Experience has indicated a need for utilizing materials for the wear-'faces of these discs having diierent degrees of compressibility and different coefficients of friction. In the plate assembly shwn in Figure 4 a two-part wearface is shown. The metal strip 1 is toothed externally at 5a for' the reason given above, and has on its top face an aixed inner circular ring 6 made of cork, and at the outer periphery of which is a spongy ring of felted fibers 2 similar t'o that shown in Figures 2 and 3. The cork piece.6 may be of cemented cork fragments, or cut from 'a continuous cork layer sheet as peeled from the bark of the cork oak tree. ln applying the cork ring 6 to the plate 1 a heavy-bodied Vcement having a low thinner or solvent ingredient is best usable. Since the cork piece may have a somewhat higher degree of compressibility, vas used in a clutch, it will be compressed during the preliminary loading of the clutch in `which it operates, and its coeicientof friction will provide initial clutch torque capacity, followed by the application of the torque in greater "proportion to the external felted ring 2. For this purpose the thicknessl dimension of the cork may be slightly 4 greater than the iinished dimension of the felt disc. uThe lower face of the plate of Fig. 4 may be ar ranged with the cork face 6a on the outer periphery and the felted ypiece 2a in the innerposition.

In the above instructions, where reference is made to the spongy felted material we are referring likewise to a material which is essentially a form of bonded paper, or cardboard. lIt is believed` worthy of comment that clutches handling a very high torque 'capacity per square inch,lequivalent to that of metal face clutches, and with less loading requirement, `have proven experimentally satisfactory, over many miles of operation such as is eX- perienced in a motor vehicle. These findings are, of course, in the use of Vclutch plates made accor-ding to the 1instructions hereinin clutch assemblies 'which are delibrately `designed to maintain a moving stream of coolling lubricant over the yfaces of the clutch discsl during the .periods of engagement and disengagement, at which times,

. otherwise, serious abrasion might occur.

l, In Figure 5 we show a composite plate 2 on the upper Iface, in which the felted material is channeled into `lands 8tl1e depth of which is approximately equal to the uvi/'idth ofthe grooves 11 between the lands, the net wear area of the lands S being taken for the required torque 4capacity of the plate. The Figure 5 showing is similar in all respects to that of Fig. 2 except that channeled plates 2 and 2a are shown. It will be observed that upon initial application of plate loading, the libers supported in their plastic sheaths will deliect under loading pressure,

a d't'here will be a small degree of lateral bulging of the Vreifenmaterial in the grooves ii, which win have Vthe effect of `"diminishing ythe amount of oil which may be trapped therein, with increase of clutch loading. The grooves 11 maybe entirely circumferential, or may be v,spir'aLfas desired for the` proper ejection of excess oil from the working area. The bases of the grooves are 4preferably ciir'ved as shown. t

, Figure 6 is to shows` the use of woven material 'in place of the felted material of the other gures, the woven n'discs 7 being pre-treated similar to'the processing given `the felted discs, having likewise a prior wetting of the thin plastic solution, followed by drying, application of 'thedense'r bonding layer plastic to the base plate 1, and when assembled ready for the oven, the piece has the A4appearance'of the Figure 6 section. It should be under- Sto'od that the degree of "mechanical pressure applied dur- 1a being wavy -as `shown in Fig. 7.

inch for heavy machinery plates, depending upon the ultimate si'ze design and power requirements of the unit in which the disc is to be installed, since under heavy compressions. and with a strong cement the bonding action will be accompanied by a squeezing of the fibers which reduces the volumetric space 'of the voids in which oil may iiow. An oil saturated plate for light Work other than for so-called heavy machinery may be formed with as little as 2 to 5 pounds per square inch, with 'the plastic solutions noted above, as for example, in a structure such as shown in Fig. l. The woven disc 7 in practice, Aprovide'sa reticulated wear-face pattern.

Figure 7 shows a special form of wavy disc la, so formed that upon initial loading, 'the torque carried by the stack of plates such as in unit A of Fig. l is first delivered by the 'small peak areas which progress in size as the discs are attened by the pressure provided from'axial motion of the pressure plate 68, for example, caused by movement of piston 66 to the left. lt should be remembered that unloaded, the mating discs are conical, and are also attened bythe loading pressure.

The wavy discs la areltitted with wear facingsin `the saine manner ias set forth above for the tiat discs.` ln

practice, it is found that the slight axialiexing of a plate so -made does not cause loosening 'of the bonded layers 4, da, because the` elted vorV composite material fiexes uniformly with the steeldisc to which it is attached;

As noted above, the plain steel clutch plates '31 in their unstressed condition may be coned, and the plates It is therefore obvious that when the loading force is applied by `either Aof the members 68 or 69 ofi-iig. l, the coned plates 31 are iiattened and the composite plates la are also flattened; `the resilient characteristics of both serving to provide a clutch release spring action.

The Fig. 44 form of composite plate shows the external sponge ring tace` 2 and the internal cork ring face 6 on the upper side, and the external cork ring face 6a and the internal sponge ring face 2a onthe lower side.

It should be observed that in assembling one of the clutch groups A or B, there are two possible methods of interleaving the sets of plates-one in which under applied loa'd `the inner cork face 6 of one side and the outer cork -face 6 of the opposite side will make initial contact with the inner and outer portions of the respective cone faces of the steel discs 31so that initial torque is sustained only by the cork faces, followed by final .full contact of both -sets of faces as the plates are flattened. The alternate arrangement -is obviously that of phasing the coned discs 351 'with respect to the inner and 'outer ring faces` of the Fig. 4 form such` that the initial rtorque is sustained only by the elted sponge faces 2 and 2a, followed by the full face contact at maximum loading compression, The designer may choose either `of these alter natives, in accordance with the desired build-up of torque to be transmitted. v

A word as to the modern theory of wet clutches is believed instructive `at this point. For many years dry Lclutch plates facedpwith organic materials, or with combinations of organic with mineral fibers, andrmolded, have been in use. Experience with this class of wearface material is that an inevitable charring of the organic 'material takes place even in an oil bath, with eventual deposition of gums `from the body or" the lubricant. This is true because of the momentary high temperatures existing on the wear-faces, during the leading cycle. "lfhermocouplel tests show that the surface fibers of suoli Vclutches must withstand momentary `temperatures far -beyondothose which organic fibers can of themselvesresist without changing their chemical nature. curnvent this phenomenon, :we have -devised the special combinations described herein in whichusefulcoefricients I To cir? achieved, at the same time yielding maximum exposure of the contact areas of the fibers to the stream of cooling lubricant. There appears to be a direct relationship between the net area of the individual fiber or particle in the clutch surface with respect to the interstitial space and the cooling effect resulting from a given velocity of lubricant moving across the clutch face. In the present invention we have not only provided for a small fiber or particle in the working surface, but also provide adjacent pores and tiny channels through which the lubricant may ush.' In the case of Figure 5 larger channels are superimposed, for the benefit of the designer who wishes to control the lubricant flow and retention with a degree of exactness.

Rather extraordinary results are obtained with clutch plates made in accordance with the instructions herein, and these results include the use of the discs as friction brakes, wherein one of the disc-holding members is nonrotatable. A further advantage appears in the relatively small size of a `clutch assembly for a given torque handling capacity, in the present invention, it being found that the overall dimension allowance for a given clutch problem may be scaled down as much as 30% below those of existing commercially used dry clutches. This saving is achieved on a dimensional basis, but a further saving appears in the provision herein of less expensive, and more easily controlled compressible materials. From the point of view of an overall economy wherein expensive metals, such as special bronzes and similar alloys are replaced by cheaper organic substances, a general benefit is conferred upon the public, in commercial use of the invention.

There are a number of plastic mixtures which are adaptable to the purposes described herein, and it is believed only necessary to show the above listed operable materials of this type, by way of example, since a designer provided these teachings would require a latitude of selection of plastics which would enable him to meet the design requirement for operating temperatures, and therefore in the above example we have provided known materials which yield proper operation in a clutch of current, standard automobile or automotive specifications.

It will therefore be seen that the composite friction unit clutch plate which we have shown and described, may be made up of various fibrous and plastic materials, and in various shapes and forms, and we therefore desire that a broad construction be placed upon our invention as a composite friction torque absorbing plate in ring form, made of fibrous substances forming the wear-faces, the fibers thereof being individually supported by thermosetting plastic sheaths and bonded to a metal backing plate by a thermo-setting bonding layer; the plate also being formable with plural wear-face rings of different fibrous structure as described above. It is therefore obvious that any changes in detail, arrangement and selection of parts may be made as above shown and described, and we therefore do not desire to be restricted in the scope of our invention except as properly limited by the appended patented claims.

We claim as our invention:

1. In a power transmission providing plural paths of torque between an engine and a load shaft, the combination comprising; a plurality of clutches for coupling or releasing the torque of said paths, at least one of said clutches consisting of mating multiple discs adapted to couple driving and driven members, said discs of one member being of plain metal and of the other member being of composite form, aV clutch lubricant circulation system, a pump caused to rotate with one of said members for supplying said system with a constantly circulating oil body, lubricant feed passages connecting said system with said multiple disc clutch, and the said composite clutch discs including fibrous wear-surfaces of spongy nature arranged to absorb and release oil flow supplied by said passages from said body during the operating cycles of said multiple disc clutch when said discs are subjected to alternate compression and loading relief.

2. A multiple disc friction clutch having one set of plain metal discs and a second set of flattenable mating discs of uniformly wavy circumferential form, each member of said secondV set comprising a disc having mounted on both wavy faces a pair of concentric rings of different frictional characteristics, the clutch structure being operative under compression loading to tiatten the assembly of the discs, so-as to provide a predetermined rise of torque capacity of said clutch proportional to the increase of said loading, said clutch structure being operative under release of said loading such that the return action of said plain discs and said wavy discs to unloaded form releases the friction rings from contact with the adjacent faces of the plain discs and a fluid pressure lubrication system operative to provide a continuous ow of lubricant oil to the said disc faces of said clutch during both engagement and disengagement of said clutch.

3. In a power transmission providing plural paths of torque between an engine and a load shaft, the combination comprising a multiple disc clutch having mating multiple discs of two alternate forms adapted to couple said engine and load shafts, said discs of one form being plain metal and of the other form being of composite form, a lubricant circulation system for said clutch, a pump driven by one of said shafts for supplying said system with a constantly'circulating oil body, lubricant feed passages connecting said system with said multiple disc clutch, the said composite clutch discs including Wearsurfaces composed of spongy fibers in a matrix operative to absorb and release oil flow supplied by said feed passages during the operating cycles of said multiple disc clutch when said discs are subjected to alternate loading compression and to relief of such loading.

4. In a power transmission clutch, the combination of a plurality of friction elements thereof adapted to transmit torque, a iluid pressure system arranged to furnish a continuous supply of lubricant oil to the Afriction faces of said elements, said clutch being composed of a selected number of said elements of two different forms alternately mated, one form of which consists of a resilient metal disc and the other form of which comprises a composite resilient disc having friction facings attached thereto on both sides thereof formed of fibrous sponge material adapted to absorb a predetermined quantity of said oil, and a loading mechanism for said device operative to compress said discs together for providing a graduated transmission of torque by said device, while causing release of an excess quantity of oil from said spongy material.

5. The power transmission clutch as claimed in claim 4 wherein said friction facings on opposite sides of said composite disc consist of an inner and outer ring of the said sponge material for loading contact with the adjacent faces of the mating metal discs, and an inner and opposite outer ring of a cork facing material for full load contact with said metal discs.

6. A friction clutch of the multiple disc type, a constant supply of lubricant oil, feed passages connecting said supply to said clutch for supplying lubricant oil thereto, driving and driven members of said clutch having one set of plain metal discs for one member and a second set of compressible mating discs of uniformly wavy circuinferential form for the other member, one of said sets comprising discs having mounted on each face a pair of concentric rings of different frictional characteristics, one of which ring pairs is composed of a material providing an oil sponge action, the clutch structure being operative under compression loading to flatten the assem- V bly of the discs and expel excess oil from the said matcrial, the deflection loading being in particular that of the wavy discs to provide a predetermined rise of torque capacity of said clutch proportional to the increase of said loading, said structure being operative under release of said loading such that the return action of said plain discs and said wavy discs to unloaded form releases the said friction rings from drive contact with the adjacent faces of the plain discs, While permitting said sponge material to rell from said oil body supplied by said 5 passages.

References Cited in the file of this patent UNITED l STATES PATENTS 10 1,493,433 y V Guay et al May 6, 1924 Germany Dec. 14, 1928 

